Manufacture of organo-substituted acids of phosphorous



Patented Sept. 19, 1950 MANUFACTURE OF ORGANO SUBSTITUTED A'CIDS OF PHOSPHOROUS .Raymond -M. Dean, Westfield, and-Edward 1P.

CashnramBayonne, N. J., assignors to Standard :01lDevelopment Company, a corporation of Delaware No Drawing. Application June 14, 1948, Serial No. 32,997

18 Claims.

This invention relates to a method of, producing disulfide .derivatives of organo-substituted thiophosphorous and thiophosphoric acids.

It is known that the organo-substituted thiophosphorous and thiophosphoric acids may be converted into corresponding disulfide compounds :by oxidation-processes in which"the hydrogen atoms-of the sulfhydrylgroupare removed, permittingtthe sulfur atoms of two acid radicals to join. Chlorine-has been proposed as an---oxidizing. agent for this purpose; but it-has been found that in practice the-chlorinealso tends to chlosrinate. the organicmportion ofthe acid molecule, and Where. this result is .not desired chlorine is an unsuitable agenthfor the purpose. 'Bromine produces siniilar results... Iodine is less objectionable; in this respect, but' its use is not economically feasible for commercial. purposes. Oxidizing agents.'containingcmetals, e. g. ferric chloride, -cupric sulfate, apermanganates, chromates, and

, the like, will react with the acid to form metal organo-thiophosphates.

In-accordance with the present invention, the oxidizing process .may be: satisfactorily carried -out without the accompaniment of side reactions fby contacting the 'aorganoethiophosphorous or organo-thiophosphoric acid with an oxide of nitrogen which has a higher proportion of oxygen 1 in ithemoleculethanxnitrous oxide (NO) .A suit- .able form o'f the-*oxide of nitrogen is the mixture "of nitrogensoxidesrrformed by the spontaneous edecomposition i-of nitronsracidrwhen thesame is liberated f-rom;a metal nitrite..:by treatment of the clatter with-a mineralacid. (These oxides contain =-nitrogen-and oxygen inianaroverall ratio of about .2c3-by 'weight. These oxides consist. largely-of thetrioxide (N203) ,cbu'tzthexdioxide:(NOzorNzOQ and higher oxides and ilowerpxides such as NO orrNzO are I believed. to "be present in minor prow-portions. wAny oftthese' oxides or mixtures of the rsaimermayifbe contacted with thetorgano-thiophosphorous or organo-thiophosphoric acid, such acid being in the liquid phase, for the purpose of producing ithe'.disulfide derivative. The reaction tiscmostconveniently carried "outv at or near room temperatures, :but the reaction may be conducted :at. \:anyntemperature "betweeni .the freezing and eboiling points of the acid of phosphorus, and un- --der,.=soime:conditionssomewhat elevated temperatures are :desirable.

I I he process of the :present invention may be rillustratedzby its application to the conversion of adi secondaryzbutyl:dithiophosphoric acid intolthe correspondingadisulfideE derivativegusing. nitrogen itriox-ideasathe oxidizinguagent. 1 The-mechanism acid, then washed with Water, and the solvent re- 2 of the reaction is represented by the following equation:

The reaction may be carried out conveniently by placing the secondary butyl thiophosphoric acid in a Milligan gas absorption-bottle or in aseries of such bottles and passing into these-absorption bottles a stream of oxides of nitrogengenerated in a separate apparatus by dropping concentrated sulfuric acid into an aqueous solution of sodium nitrite. After the oxidation reaction has been completed the reaction product, conveniently diluted with a solvent such as naphtha, is washed with a dilute aqueous alkali solution to remove unreacted secondary butyl thiophosphoric moved under vacuum.

The process of the present invention may be applied to the conversion'of any acid of the formula ll (ROMPSH where R is any hydrocarbon radical, e. g., an alkyl, alkenyl, cycloalkyl, aryl, alkaryl, oraralkyl group, and n is-O or 1, into the corresponding disulfide derivative of the formula nom ssl romi Where R and n have the same meaning as above.

The organo-substituted thiophosphorous and thiophosphoric acids may be prepared by known means, for example, by reacting an alcohol or phenol with a sulfide of phosphorus. Examples of the acids of phosphorus which may readily be converted into the disulfide products in accordance with the present invention include di-ethyldithiophosphoric acid, di-n-propyldithiophosphoric acid, di-isopropyldithiophosphoric acid, disec.-butyldithiophosphoric acid, di-sec.-butylthiophosphorous acid, di-octyldithiophosphoric acid, di-stearyldithiophosphoric acid, di-oleyldithiophosphoric acid, di-(tert.-octylphenyl)dithiophosphoric acid, di-(tert.-octylphenyl)thiophosphorous acid, di-benzyldithiophosphoric acid, and the like. The invention has particular application in the conversion of acids in which the organic group is an alkyl group containing 2 to 8 carbon atoms per molecule.

The following example illustrates in detail the application of the present invention to the conversion of di-n-propyldithiophosphoric acid into the disulfide derivative.

Example 1 Two Milligan gas absorption bottles containing a total of 350 g. of di-n-propyldithiophosphoric acid were connected in series, the bottle nearest the gas generator containing 200 g. and the other bottle containg 150 g. Nitrogen oxides were generated in a separate reaction vessel by adding 18 g. of concentrated sulfuric acid to g. of sodium nitrite dissolved in ml. of water over a period of 4 hours. These nitrogen oxides were mixed with nitrogen gas and led through the acid of phosphorous as they were generated, the mixture containing approximately 35 parts by volume of nitrogen to 1 part by volume of nitrogen oxides. used in the process. After the oxidation step, which was conducted at room temperature, had been completed the reaction mixture contained in the gas absorption bottles was dissolved in 200 ml. naphtha and washed twice with aqueous 10% caustic alkali solution to remove unreacted acid. After further washing with water until the washings were neutral and removing the naphtha under vacuum at 200 F., 73 g. of di-n-propylthiophosphoric disulfide was recovered. This represents a yield of 95% based on the amount of sodium nitrite used in generating the nitrogen oxides. The product was a liquid of about 90 seconds viscosity Saybolt at 100 F. and about to 1 Robinson color.

The process of the present invention may be carried out, if preferred, by generating the nitrogen oxides in the reaction mixture containing the organo-thiophosphorous or organo-thiophosphoric acid. For example, an aqueous solution of sodium nitrite may be mixed with the acid of phosphorous and a mineral acid, e. g., sulfuric acid, may be, added slowly to liberate the oxides of nitrogen. These oxides will immediately react with the acid of phosphorous to produce the disulfide derivative of the latter. For optimum yields, the alkali metal nitrite and mineral acid are each added in an amount which is a molecular equivalent of the acid of phosphorous present. This method may be illustrated by the following three examples.

Example 2 200 g. of di-secondary butyl dithiophosphoric acid was placed in a flask equipped with a stirrer, thermometer, and reflux condenser. An aqueous solution consisting of 18 g. sodium nitrite dissolved in 75 ml. water was added at 90 F. over a period of 1 hour. 13 g. of sulfuric acid was then added at the same temperature over a period of 1 hour. During this process nitrogen was blown through the reaction vessel at about 2 to 3 cu. ft. per hour for the purpose of excluding air during the oxidation step. The reaction product was then diluted with 200 m1. naphtha, washed twice with 5% aqueous sodium hydroxide solution, andthen with water until the washings were neutral,

and the naphtha stripped off under vacuum at 200 F. A yield of g. of (ii-secondary butyl thiophosphoric acid disulfide was obtained. The product was a fluid oil of about seconds viscosity Saybolt at F., neutralization number 0.6, Robinson color, and conta ned. 2.91 sulfur.

Approximately 5 cu. ft. of nitrogen was Example 3 222 g. (1 mol.) of phosphorous pentasulfide was charged into a 3-liter 4-necked flask equipped with a dropping funnel, thermometer, suitable agitator and a gas outlet. 330 g. (4:4 mols) of secondary butyl alcohol was added and the temperature raised slowly to 220 F. over a period of 2 hours. After cooling to F., 138 g. (2 mols) of sodium nitrite dissolved in 250 ml. of water was added over a period of 30 minutes, keeping the temperature below F. 102 g. (1 mol) of 98% sulfuric acid was then added over a period of 1 hour, after which the temperature was raised to F. and held at this point for an additional hour. After dilution with 200 m1. naphtha and washing twice with 5% aqueous sodium hydroxide solution the product was recovered by high vacuum distillation at 200 F. A product weighing 404 g. and consisting of a wine colored oil resulted. The product showed a neutralization number of 0.25, a Robinson color reading of 8 and a sulfur content of 29.3%.

Example 4 22 lbs. 3 oz. (1 mol) of phosphorous pentasulfide was charged into a 30 gallon glass lined Pfaudler reactor. 26 lbs. 6 oz. (4.4 mols) of n-propyl alcohol was added. The temperature was raised to 200 F. over a period of 1 hour and held at this point for 2 hours additional. After cooling to 90 F., 13 lbs. 13 oz. (2 mols) of sodium nitrite dissolved in 2 gallons of water was added at 90 F. over a period of 1 hour. 3 oz. (1 mol) of 98% sulfuric acid was then added over a period of 1 hour at 90 F. After adding 4 gallons of naphtha the reaction mixture was stirred for hour, after which it was meshed 3 times with 5% sodium hydroxide and twice with Water. The produce was recovered by high vacuum distillation at 200 F. 38 lbs. of a wine colored product resulted, having a neutralization number of 3.2, a Robinson color-reading of 4 /2+, and a sulfur content of 31.4%. V.

In a modification of the process of the present invention the oxide of nitrogen may be mixed with air or oxygen when contacting the organosubstituted acid of phosphorus, or air or oxygen may be passed through the reaction mixtur when the oxide of nitrogen is generated in the presence of the acids of phosphorus. When oxygen is present the lower oxide of nitrogen resulting from the oxidation reaction is again converted into a higher oxide of nitrogen, which again Considering nitrogen trioxide (N203) as the oxidizing agent, when the oxidizing reaction takes place this is reduced to nitric oxide (NO) in accordance with the equation shown above. When oxygen is present, the nitric oxide is again converted into nitrogen trioxide in accordance with the equation Thus, in effect, the oxygen is the ultimate oxidizing agent. This modification of the process has advantages in reducing the amounts of oxides of nitrogen required in commercial operations, since with a small amount of oxides of nitrogen large conversions of organo-substituted acids of phosphorus to the disulfide can be accomplished.

As to the amounts of oxygen which should be present in this modification of the process of the invention, no specific proportions relative to the amounts of oxides of nitrogen are required for 75 the operation. Since the process can be carried.

10 lbs.

w obtained in Ex out without any ox I, se rresent heamou s. 9 fi ditdiifesi t gl a amounts o*'-'quant1t1es several times that of the nitrogen oxides present in proportions by volume. Generally, when air isrnixed with oxidesoi nitrogen, ratios of lto"60 -vtiliiirie's"ofitintd'one 1 volume of oxides of nitrogen are preferred, although the invention is not limited to these ratios.

i T difi ro e s1is llvsfi aie zba he iq lqwrams b tt e IT'ADDiQXi matelylfi cu. ft; of air conta n g the oxidesof iii ee' e r d" 1 1 a eee t gs' ti h ves frcni ycrspd m nitrite and iagyqrgsuifuric acidjrepresenting a ratio offal t '35 parts 12.x vo um o a id-h ne: tibv vo fiI fbrn bottles Velf ta periodjof 5 hours at so 'iqogr'i The product wa finished as in Example 1,

similar malnher', the ai'dvantagesof using oxygen are apparent.

(1) A reaction was carried out in the manner describediniuf'but with no oxide of nitrogen present. This resulted in no yield of the sulfide product, indicatingthat'oxygen "alone is not an effective oxidizing agent;

Er mrle 6 The process of Example 2 was carried out, us ing the materials inquantitiesstated therein "and other conditions-of the reaction being the same, bu'uni "th'firesent case 'air was blownthrough the reactioriymixture"; continuously during the a totalamountof abputfi cu. ft. 'n e e r lio iien "volu e of ieldof. 174 U thiopho sphoricacid .disulfidel It' will be recalled that only 80 g. "of the product was obtained in Example 2, where air was excluded from the reaction zone.

The disulfide derivatives of organo-substituted thiophosphorous and thiophosphoric acids produced in accordance with the process of the present invention are useful as additives for mineral lubricating oils, to which they impart oxidation resisting properties.

This invention is not to be considered as limited in scope by any of the foregoing examples, which are included for illustrative purposes only, but is to be limited solely by the terms of the appended claims.

What is claimed is: l. A method of converting an acid selected y eld of, 235; g: crime from the class consisting of acids of the formulaand acids of the formula- S (ROh SH (R0) 2PSSP(OR) 2 and compounds of the formulawhere R has the meaning given above, which comprises contacting saidlcid while in a liquid phase with an oxideof nitrogen having a higher proportion of oxygen in the molecule than nitrous oxide (NO).

2. A method according to claim 1 in which R of the formula is analkyl group.

3. A method according to claim 1 in which R, of the formula is an" alkyl group containing 2 to 8 carbon atoms pr molecule.

'4. A methodaccording to claim 1 in which the oxide of nitrogen is employed in a"mixture of oxides of nitro'gen'in which the ratidof nitrogen to oxygen is about 2:3 by Weight. 5. A method .of converting di-n -propyldithiophosphoric acid intoiadisulfide derivativethereo'f which comprises generating oxides of nitrogen by adding sulfuric "acid to an aqueous solution of sodium nitrite and contacting the oxides of nitrogen so generated, With'sa'id' 'di n-propyldi thiophosphoricacidat'rooriiternperature.

'6. A. method of converting an acid selected from the class consisting of acids of the formula (BO) zPSll and acids of, the formula i (R O)2P sH where R is any hydrocarbon radical, into the corresponding'disulfide derivative 'of the class consisting of compounds ,qithe formu1a raonessmomz and compounds of the formula i (RO)zPSSP(OR)2 where R has the meaning given above, which comprises adding a mineral acid to a liquid mixture of said acid of phosphorus and an aqueous solution of an alkali metal nitrite.

7. A process according to claim 6 in which the mineral acid is sulfuric acid and in which the alkali metal nitrite is sodium nitrite.

8, A method according to claim 6 in which R of the formula is an alkyl group, in which the mineral acid is sulfuric acid, and in which the alkali metal nitrite is sodium nitrite.

9. A method which comprises adding an aqueous solution containing two molecular proportions of sodium nitrite to one molecular proportion of di-secondary butyl dithiophosphoric acid and subsequently adding to the mixture thus formed one molecular proportion of sulfuric acid.

10. A method which comprises adding an aqueous solution containing two molecular proportions of sodium nitrite to one molecular proportion of di-n-propyldithiophosphoric acid, and subsequently adding to the mixture thus formed one molecular proportion of sulfuric acid.

11. A' method of converting an acid selected from the class consisting of acids of the formula- (RO)2PSH and acids of the formula-- II (RO)zPSH where R, is any hydrocarbon radical, into the corresponding disulfide derivative of the class consisting of compounds of the formulaand compounds of the formulas (ROhi SSI tORM where R has the meaning given above, which comprises contacting said acid, while in the liquid phase with an oxide of nitrogen having a greater proportion of oxygen in the molecule than nitrous oxide (NO), in the presence of oxygen.

12. A method according to claim 11 in which R of the formula is an alkyl group.

13. A method according to claim 11 in which R of the formula is an alkyl group containing 2 to 8 carbon atoms per molecule.

14. A method according to claim 11 in which the oxide of nitrogen is employed in a mixture of oxides of nitrogen in which the ratio of nitrogen to oxygen is about 2:3 by weight.

15. A method which comprises contacting disecondary butyl dithiophosphoric acid while in the liquid phase with a mixture of an oxide of nitrogen having at least as-great a proportion of oxide in the molecule as nitrogen trioxide (N203) and 10 to 60 times the amount of said oxid of nitrogen by volume of air at a temperature of 80100 F.

16. A method of converting an acid selected from the class consisting of acids of the formula- (R0) zPSH and acids of the formula (Rohl sH where R, is any hydrocarbon radical, into the corresponding disulfide derivative of the class consisting of compounds of the formula- (RO) 2PSSP(OR) 2 and compounds of the formula-- s s noni ssi wmi where R has the meaning given above, which comprises adding a mineral acid to a liquid mixture of said acid of phosphorus and an aqueous solution of an alkali metal nitrite while passing a gas containing free oxygen through the reaction mixture.

17. A method according to claim 16 in which R of the formula is an alkyl group containing 2 to 8 carbon atoms per molecule, in which the mineral acid is sulfuric acid, in which the alkali metal nitrite is sodium nitrite, and in which the gas containing free oxygen is air.

18. A method which comprises adding to one molecular proportion of di-secondary butyl dithiophosphoric acid in a reaction vessel a concentrated aqueous solution containing about onefourth molecular proportion of sodium nitrite at 90 F., subsequently adding to the mixture thus formed about one-eighth molecular proportion of sulfuric acid at 90 F., and during the addition of the said sodium nitrite and sulfuric acid passing air continuously through the reaction mixture.

RAYMOND M. DEAN. EDWARD P. CASHMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,763,852 Johnson June 17, 1930 2,060,815 MacAfee Nov. 17, 1936 2,298,387 Kenton et a1. Oct. 13, 1942 OTHER REFERENCES Lassar-Cohn, Arbeitsmethoden fur Organisch- Chemische Laboratorienj,Spezieller Teil (5th ed., 1923) pages 626, 751-754 and 770.

Ephraim, Inorganic Chemistry (94th rev. ed., by Thorne and Roberts, 1943), pages 668-674. 

1. A METHOD OF CONVERTING AN ACID SELECTED FROM THE CLASS CONSISTING OF ACIDS OF THE FORMULA- 